Added RUSTUP_TOOLCHAIN to tox passenv

Author: alex

tox.ini

@@ -10,7 +10,7 @@ deps =
     -e ./vectors
     pytest-shard>=0.1.2
     randomorder: pytest-randomly
-passenv = ARCHFLAGS LDFLAGS CFLAGS INCLUDE LIB LD_LIBRARY_PATH RUSTFLAGS CARGO_TARGET_DIR LLVM_PROFILE_FILE OPENSSL_FORCE_FIPS_MODE
+passenv = ARCHFLAGS LDFLAGS CFLAGS INCLUDE LIB LD_LIBRARY_PATH RUSTFLAGS CARGO_TARGET_DIR LLVM_PROFILE_FILE OPENSSL_FORCE_FIPS_MODE RUSTUP_TOOLCHAIN
 commands =
     pip list
     !nocoverage: pytest -n auto --cov=cryptography --cov=tests --durations=10 {posargs} tests/